1. Field of the Invention
The present invention relates to an ink jet apparatus used for a printer and the like and, more particularly, to an ink jet apparatus which is constructed in such a way that an otherwise poor discharge in a nozzle for ink jet can be improved by suction.
2. Description of the Prior Art
An ink jet printer provided with an ink jet apparatus discharges an ink or liquid or liquid-droplets to print dots on a printing paper for formation of a letter, character, figure, image, and the like. Therefore, the ink jet printer is provided with an ink tank and the like.
Consequently, portable compact electronic apparatuses which have such an ink jet printer have various problems different from electronic apparatuses, such as data-terminal and the like, which are hardly transported. For example, poor discharge of ink is caused by retrogradation of meniscus of ink in a nozzle, invasion of air bubbles into the nozzle, fixation of ink, and the like due to impact or vibration on transportion of the portable apparatuses which have the ink jet printer inclined therein.
In case that an electronic apparatus loading an ink jet printer is left standing in a packing state or transported in unused state for a long period of time, solvents in an ink, such as water and the like, evaporate from the tubes for which supply the ink and the like. Therefore, continuous supply of the ink is obstructed by an increase of the volume of air within a system for supply of the ink. Accordingly, there is a risk of non-discharge of ink owing to consumption of only ink remaining in a sub-tank.
In order to dissolve the above-mentioned disadvantages, U.S. Patent No. 4,263,030/1981, German patent application No. 3119892.9, and the like have already proposed a process which prevents poor discharge of ink by suction due to negative pressure. FIGS. 1 and 2 illustrate such suction process. In FIGS. 1 and 2, a numeral 1 shows an ink jet nozzle unit whose the rear end is in communication with an ink in a sub-tank 2. The sub-tank 2 is connected with a bag-like main tank 5 through an ink-supplying port 3 by a tube 4.
An end of the sub-tank 2 is connected to a pump 8 for improvement of poor discharge as mentioned below by a tube 7 through a vent hole 6. In the path of the tube 7, a filter 9 is provided to limit a flow amount of the ink from the sub-tank 2.
On the tip of the nozzle unit 10 is mounted a removable cap capable of always closing the tip of the nozzle when the tip is not in use, protecting the nozzle, and preventing the nozzle from drying and preventing foreign matter from attaching. An end of a tube 11 is connected to the cap 10 and the other end of the tube 11 with the pump 8.
The pump 8 is provided with a piston 12 whose peripheral surface is closed by O-rings O.sub.1. A rod 13 of the pump 8 is closed by an O-ring O.sub.2.
In addition, the piston 12 is biased upwards by a spring 14. A discharge hole 15 is disposed in a portion of the piston 12. A valve 17 is mounted on the under end of the discharge hole and the upper end thereof is in communication with a suction chamber 16.
In the above-mentioned construction, the piston 12 is located at the upper limit by the spring 14 in the starting state of the pump 8 as shown in FIG. 1. Accordingly, the volume of the suction chamber 16 is minimum. When the piston 12 is moved downwards from the starting position and overcomes the force of the spring 14, the volume of the suction chamber 16 increases to cause negative pressure. The negative pressure is led to the sub-tank 2 and the nozzle unit 1 through tubes 7 and 11. At this time, the valve 17 is closed. FIG. 2 shows the above-mentioned state. When the negative pressure is caused as mentioned above, the pressure in the sub-tank 2 also lowers so that an ink is sucked from the main tank 5 and the ink in the nozzle unit 1 is sucked simultaneously. Consequently, discharge of ink can be recovered. Therefore, at the beginning of printing, inability of ink discharge does not occur and printing can immediately be started by carrying out the above-mentioned movement immediately before the beginning of the operation of the ink jet printer.
However, the above-mentioned apparatuses still have the following disadvantages. In other words, the side of the sub-tank 2 has sufficient negative pressure only when a level of the liquid exists in the vicinity of the vent hole 6 as the liquid level represented by H.sub.1 in FIG. 1. When the liquid level lowers at a lower position than the ink-supplying port 3, the space in the sub-tank 2 is nearly equal to the maximum volume of the suction chamber 6 or more. Therefore, the ratio of change in the volume of the air in the side of the pump 8 is substantially reduced so that the negative pressure caused by the suction becomes near atmosphere. As the result, the ink can not be sufficiently sucked from the nozzle unit 1 so that poor discharge is not improved.